Republican presidential candidate Donald Trump speaks to supporters in Fort Worth, Tex., on Friday. (LM Otero/Associated press)

It is the great, democratic virtue of presidential campaigns that they subject candidates to every kind of stress, eventually revealing their core, their character. For Donald Trump, the test has been political success. After leading the Republican field for six months, and in some quarters receiving adulation nearly equal to his self-regard, how has Trump responded? Has he been sobered? Have his rhetoric and temperament matured?

No. Decidedly, no. The realistic prospect of executive power has only increased Trump’s swagger. He has threatened a Republican donor who opposes him. “I hear the [Ricketts] family,” he tweeted, “who own the Chicago Cubs, are secretly spending $’s against me. They better be careful, they have a lot to hide!”

Trump has threatened the media, promising to “open up our libel laws” so he can more easily sue outlets that differ in their view of the truth about him. “I think the media is among the most dishonest groups of people that I’ve ever met. They’re terrible.” he said recently. Referring specifically to The Post, he added: “If I become president, oh, do they have problems. They’re going to have such problems.”

Trump has attempted to smear and intimidate a district judge, Gonzalo Curiel, who is presiding over a lawsuit for fraud against Trump University, with its distinguished faculty of cardboard cutouts and allegedly bankrupt real estate investors. Trump accuses Curiel of hostility against him because “I’m very, very strong on the border.” Another shrill pipe of the ethnic dog whistle.

This is more than a personality disorder talking. Trump roots his intimidation in a worldview — the need for the strong hand. It is the most consistent commitment of Trumpism. As early as 1990, Trump criticized Soviet leader Mikhail Gorbachev for not having a “firm enough hand.” He cited China’s butchers of Tiananmen Square as examples of his conception of power: “They were vicious, they were horrible, but they put it down with strength. That shows you the power of strength. Our country is right now perceived as weak . . . as being spit on by the rest of the world.” Following allegations last year that Russian leader Vladimir Putin had killed several high-profile journalists, Trump responded, “He’s running his country and at least he’s a leader, unlike what we have in this country.”

Many pundits once said Donald Trump never had a chance. But despite the Republican frontrunner's politically incorrect comments on Mexicans, Muslims and his closest rivals, his popularity is soaring. (Reuters)

And Trump’s supporters seem to welcome this aspect of his appeal. According to a Vox analysis of the South Carolina Republican primary vote, the best statistical predictor of Trump support is an inclination toward authoritarianism — a belief in the need for “aggressive leaders and policies.” So Trump, if he wins the nomination and the presidency, will feel a mandate for his menace.

There is a moment in the 1957 movie “A Face in the Crowd” when a TV personality turned power-mad sociopath, Larry “Lonesome” Rhodes, says, “I’m not just an entertainer. I’m an influence, a wielder of opinion, a force . . . a force!” On the evidence, Trump is reaching that point of intoxication.

We have seen the lengths to which Trump will go to threaten and intimidate his enemies, armed mainly with social media. It seems reckless beyond reason — reckless with the republic itself — to arm him with the immense power of the executive branch. Consider the inherently threatening quality of the words “Trump’s military” or “Trump’s FBI” or “Trump’s IRS.” The grant of vast influence to a leader of such vindictive temperament is utterly frightening.

In a certain way, Trump may be excused for his adolescent view of strength — the power of the tantrum, of the crude put-down, of the dirty trick. Trump has no evident knowledge of American history or of a conservative ideology. He lives only in the vivid present of his wants and needs. He is squandering an inheritance he does not value, that he does not even understand.

But what excuse can be made for New Jersey Gov. Chris Christie? His endorsement of Trump was evidently made out of pique and ambition. It is humiliating for the governor of a great state to make himself the subordinate of — the junior partner to — a cut-rate Mussolini. Christie has, in the past, shown leadership on entitlement reform and the fair treatment of Muslims. Now his enduring reputation will be a willingness to swallow any foolishness, any prejudice, to serve the cause of Christie.

Trump’s conception of leadership is to become large by making others small. In a reality television star, this is a job qualification. In a president, it would raise the prospect of serious damage to our democratic system.

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Donald Trump hinted on Feb. 28 that he might run as an independent, because the GOP is treating him "unfairly." It's not the first time he's made that threat. (Peter Stevenson/The Washington Post)